Equipment
Reverse osmosis (RO)
Pressure-driven filtration through a semi-permeable membrane. First-stage filter in most pure-water cleaning rigs.
A filtration method where water is pushed under pressure through a semi-permeable membrane that rejects dissolved minerals. The membrane catches calcium, magnesium, sodium, and most other dissolved solids while letting pure water through. Used in home under-sink water filters and in commercial water-treatment rigs.
For pure-water window cleaning, RO is typically the first stage (cheap per gallon, high volume) feeding a DI polishing stage (expensive per gallon, but low volume since RO already did most of the work).